When a voluntary muscle makes a voluntary movement, a muscle action potential occurs in the muscle. There is known an evaluation system which evaluates a composition and an activity status, such as fatigue, of a muscle on the basis of the position of a body surface where a muscle action potential is detected, and propagation velocity and the like of the muscle action potential. FIG. 5 shows a related evaluation apparatus 100. A plurality of myoelectric detection electrodes 101 are brought into close contact with a body surface 120 of a muscle 110, and muscle action potentials are detected from the respective myoelectric detection electrodes 101. A degree of fatigue of the muscle is evaluated from propagation velocity (muscle fiber conduction velocity: MFCV) of the muscle action potentials along muscle fibers 110a (Non-Patent Literature 1).
As shown in FIG. 5, a motor command from the central nervous system initially propagates as electric excitation to neuromuscular junctions 112a through motor axons 112. Acetylcholine emitted from the nerve endings acts on the end-plates on the muscle fiber side of the neuromuscular junctions 112a. Muscle action potentials occur thus at the end-plates when the voluntary muscle contracts. In general, the neuromuscular junctions (end-plates) 112a lie in the center of the muscle fibers 110a. The muscle action potentials occurring in the neuromuscular junctions 112a propagate from the center of the muscle fibers 110a to both sides in a longitudinal direction of the muscle 110 along the muscle fibers 110a. In the evaluation apparatus 100, myoelectric detection electrodes 101 are put in close contact with a plurality of positions on the body surface 120 along the direction of the muscle fibers 110a from the neuromuscular junctions 112a to a peripheral side. A difference between muscle action potentials detected from a pair of myoelectric detection electrodes 101, 101 adjoining in the direction of arrangement will be referred to as a muscle action potential detected by the pair of myoelectric detection electrodes. Muscle action potentials detected by respective pairs are plotted on an electromyogram with the horizontal axis as a time axis. The propagation velocity MFCV of the muscle action potentials is determined from the electromyogram.
For the purpose of rehabilitation, there is known a rehabilitation support system which applies an electrical stimulation signal to a muscle to expand and contract the muscle for training. A plurality of biomedical electrodes are brought into close contact with the body surface of the muscle to be trained, and an electrical stimulation signal is applied to the muscle inside the body surface via the biomedical electrodes to forcefully expand and contract the muscle. To evaluate the efficiency and effect of training of the muscle by the electrical stimulus, a relationship between the position of the electrical stimulus and the patient's reaction caused by the electrical stimulus is recorded upon each training session, and an evaluation is made on the basis of the transition of the relationship. For accurate comparison of changes in reaction, the biomedical electrodes need to be put in close contact with the same positions on the body surface in each training session. Patent Literature 1 describes a rehabilitation support system which obtains positions where biomedical electrodes are put in close contact with a body surface from a triangular shape of the body's outline, marks attached to the body, an auxiliary scale, feature points on the body, etc. The rehabilitation support system displays the close contact positions of the biomedical electrodes along with an image showing the body surface, so that the biomedical electrodes are guided into close contact with the same positions on the body surface in the next training session of the muscle.